Intestinal epithelial tuft cell induction is negated by a murine helminth and its secreted products

Helminth parasites are adept manipulators of the immune system, using multiple strategies to evade the host type 2 response. In the intestinal niche, the epithelium is crucial for initiating type 2 immunity via tuft cells, which together with goblet cells expand dramatically in response to the type 2 cytokines IL-4 and IL-13. However, it is not known whether helminths modulate these epithelial cell populations. In vitro, using small intestinal organoids, we found that excretory/secretory products (HpES) from Heligmosomoides polygyrus blocked the effects of IL-4/13, inhibiting tuft and goblet cell gene expression and expansion, and inducing spheroid growth characteristic of fetal epithelium and homeostatic repair. Similar outcomes were seen in organoids exposed to parasite larvae. In vivo, H. polygyrus infection inhibited tuft cell responses to heterologous Nippostrongylus brasiliensis infection or succinate, and HpES also reduced succinate-stimulated tuft cell expansion. Our results demonstrate that helminth parasites reshape their intestinal environment in a novel strategy for undermining the host protective response.

Enteric helminth coinfection enhances host susceptibility to neurotropic flaviviruses via a tuft cell-IL-4 receptor signaling axis

Although enteric helminth infections modulate immunity to mucosal pathogens, their effects on systemic microbes remain less established. Here, we observe increased mortality in mice coinfected with the enteric helminth Heligmosomoides polygyrus bakeri (Hpb) and West Nile virus (WNV). This enhanced susceptibility is associated with altered gut morphology and transit, translocation of commensal bacteria, impaired WNV-specific T cell responses, and increased virus infection in the gastrointestinal tract and central nervous system. These outcomes were due to type 2 immune skewing, because coinfection in Stat6-/- mice rescues mortality, treatment of helminth-free WNV-infected mice with interleukin (IL)-4 mirrors coinfection, and IL-4 receptor signaling in intestinal epithelial cells mediates the susceptibility phenotypes. Moreover, tuft cell-deficient mice show improved outcomes with coinfection, whereas treatment of helminth-free mice with tuft cell-derived cytokine IL-25 or ligand succinate worsens WNV disease. Thus, helminth activation of tuft cell-IL-4-receptor circuits in the gut exacerbates infection and disease of a neurotropic flavivirus.

SLAM family receptors control pro-survival effectors in germinal center B cells to promote humoral immunity

Expression of the signaling lymphocytic activation molecule (SLAM)-associated protein (SAP) is critical for the germinal center (GC) reaction and T cell-dependent antibody production. However, when SAP is expressed normally, the role of the associated SLAM family receptors (SFRs) in these processes is nebulous. Herein, we established that in the presence of SAP, SFRs suppressed the expansion of the GC reaction but facilitated the generation of antigen-specific B cells and antibodies. SFRs favored the generation of antigen-reactive B cells and antibodies by boosting expression of pro-survival effectors, such as the B cell antigen receptor (BCR) and Bcl-2, in activated GC B cells. The effects of SFRs on the GC reaction and T cell-dependent antibody production necessitated expression of multiple SFRs, both in T cells and in B cells. Hence, while in the presence of SAP, SFRs inhibit the GC reaction, they are critical for the induction of T cell-mediated humoral immunity by enhancing expression of pro-survival effectors in GC B cells.

NK cell recruitment limits tissue damage during an enteric helminth infection

Parasitic helminths cause significant damage as they migrate through host tissues to complete their life cycle. While chronic helminth infections are characterized by a well-described Type 2 immune response, the early, tissue-invasive stages are not well understood. Here we investigate the immune pathways activated during the early stages of Heligmosomoides polygyrus bakeri (Hpb), a natural parasitic roundworm of mice. In contrast to the Type 2 immune response present at later stages of infection, a robust Type 1 immune signature including IFNg production was dominant at the time of parasite invasion and granuloma formation. This early response was associated with an accumulation of activated Natural Killer (NK) cells, with no increase of other innate lymphoid cell populations. Parabiosis and confocal microscopy studies indicated that NK cells were recruited from circulation to the small intestine, where they surrounded parasitic larvae. NK cell recruitment required IFNγ receptor signaling, but was independent of CXCR3 expression. The depletion of tissue-infiltrating NK cells altered neither worm burden nor parasite fitness, but increased vascular injury, suggesting a role for NK cells in mediating tissue protection. Together, these data identify an unexpected role for NK cells in promoting disease tolerance during the invasive stage of an enteric helminth infection.

Helminth Interaction with the Host Immune System: Short-Term Benefits and Costs in Relation to the Infectious Environment

Chronic infections imply that the parasite and the host immune system closely interact for a long time without a fatal outcome. Environmental changes encountered by hosts and parasites, such as coinfections, can deeply affect the stability of this apparent equilibrium. Our study aimed to determine the effect of the infectious environment on the costs and benefits of chronic infection with the gut nematode Heligmosomoides polygyrus in mice. Heligmosomoides polygyrus is known for its capacity to actively interfere with the host immune response by secreting molecules that can dampen immunity. We simulated bacterial coinfection of H. polygyrus-infected CBA-strain mice during the chronic phase of the infection by injecting them with Escherichia coli lipopolysaccharide. We found that infection by H. polygyrus induced only weak costs for the host (in terms of reproductive investment) and was characterized by the upregulation of both Th1 (interferon-γ) and anti-inflammatory (transforming growth factor-β) cytokines, which is favorable to parasite persistence. However, when co-occurring with the simulated bacterial infection, H. polygyrus infection was associated with a pronounced shift toward a pro-inflammatory status, which was deleterious to both the parasite and the host. Our study highlights the dynamic equilibrium reached during chronic infection, where a rapid environmental change, such as a concomitant bacterial infection, can deeply affect the outcome of the host-parasite interaction.

Heligmosomoides polygyrus: EAE remission is correlated with different systemic cytokine profiles provoked by L4 and adult nematodes

Primary exposure of mice to gastrointestinal nematode infection with Heligmosomoides polygyrus reduces inflammation in an experimental model of multiple sclerosis. In this study, we aimed to evaluate the ability of H. polygyrus L4 larvae and adults infection to reduce the symptoms of ongoing experimental autoimmune encephalomyelitis (EAE) in female C57Bl/6 mice. EAE was induced by myelin oligodendrocyte glycoprotein MOG(p35-55) and after 21 days mice were orally infected with 200 infective larvae (L3) of H. polygyrus. Reduction in EAE symptoms was observed from 2 days post infection and the symptoms were almost completely inhibited at 6 days post infection. This effect was associated with limited total protein content in the cerebrospinal fluid; CSF, and significant decreased pro-inflammatory IL-12p40 concentration and increased concentration of the regulatory cytokines IL-10, TGF-β and IL-6 in the CSF and in the serum. The reduction of EAE symptoms in the enteral phase was associated with higher IL-12p40 concentration in the CSF and very low concentrations of IL-17A and IL-2 in the serum. The fourth stage of gastrointestinal nematode can reverse systemic inflammation in animal models of multiple sclerosis by reducing IL-12 and promoting regulatory cytokines production. The mechanism induced by adult nematodes which sustained EAE inhibition can be provoked by regulatory mechanism connected with reduce IL-17A concentration.

Characterisation of effector mechanisms at the host:parasite interface during the immune response to tissue-dwelling intestinal nematode parasites

The protective immune response that develops following infection with many tissue-dwelling intestinal nematode parasites is characterised by elevations in IL-4 and IL-13 and increased numbers of CD4+ T cells, granulocytes and macrophages. These cells accumulate at the site of infection and in many cases can mediate resistance to these large multicellular pathogens. Recent studies suggest novel potential mechanisms mediated by these immune cell populations through their differential activation and ability to stimulate production of novel effector molecules. These newly discovered protective mechanisms may provide novel strategies to develop immunotherapies and vaccines against this group of pathogens. In this review, we will examine recent studies elucidating mechanisms of host protection against three widely-used experimental murine models of tissue-dwelling intestinal nematode parasites: Heligmosomoides polygyrus, Trichuris muris and Trichinella spiralis.

Infection with parasitic nematodes confounds vaccination efficacy

T helper (Th) cells produce signature cytokine patterns, induced largely by intracellular versus extracellular pathogens that provide the cellular and molecular basis for counter regulatory expression of protective immunity during concurrent infections. The production of IL-12 and IFN-gamma, for example, resulting from exposure to many bacterial, viral, and protozoan pathogens is responsible for Th1-derived protective responses that also can inhibit development of Th2-cells expressing IL-4-dependent immunity to extracellular helminth parasites and vice versa. In a similar manner, concurrent helminth infection alters optimal vaccine-induced responses in humans and livestock; however, the consequences of this condition have not been adequately studied especially in the context of a challenge infection following vaccination. Demands for new and effective vaccines to control chronic and emerging diseases, and the need for rapid deployment of vaccines for bio security concerns requires a systematic evaluation of confounding factors that limit vaccine efficacy. One common albeit overlooked confounder is the presence of gastrointestinal nematode parasites in populations of humans and livestock targeted for vaccination. This is particularly important in areas of the world were helminth infections are prevalent, but the interplay between parasites and emerging diseases that can be transmitted worldwide make this a global issue. In addition, it is not clear if the epidemic in allergic disease in industrialized countries substitutes for geohelminth infection to interfere with effective vaccination regimens. This presentation will focus on recent vaccination studies in mice experimentally infected with Heligmosomoides polygyrus to model the condition of gastrointestinal parasite infestation in mammalian populations targeted for vaccination. In addition, a large animal vaccination and challenge model against Mycoplasma hyopneumonia in swine exposed to Ascaris suum will provide a specific example of the need for further work in this area, and for controlled field studies to assess the impact of other similar scenarios.

ANHYDROBIOSIS INCREASES SURVIVAL OF TRICHOSTRONGYLE NEMATODES

This study demonstrates that infective-stage larvae of 2 trichostrongyle ruminant gastrointestinal nematodes, Haemonchus contortus and Trichostrongylus colubriformis, can enter into anhydrobiotic states when completely desiccated. Larvae of control trichostrongyle species, Heligmosomoides polygyrus and Nippostrongylus brasiliensis, that infect mice were unable to survive desiccation or to enter into anhydrobiosis. Ruminant larvae were able to survive up to 7 desiccation/rehydration cycles, and, during anhydrobiosis, metabolic activity was decreased and survival of the larvae was prolonged both in the laboratory and in the field. Relative humidity had no effect on ruminant larval survival after anhydrobiosis compared with controls. Temperature had a significant effect, 85.8 +/- 2.3% of larvae in anhydrobiosis could survive low temperatures (0 C) that killed all control larvae. Metabolic activity, measured by changes in lipid content and CO2 respiration, was significantly lower in larvae that entered anhydrobiosis compared with controls (P < 0.05). In field experiments using open-meshed chambers under ambient environmental conditions, larvae in anhydrobiosis had significantly higher survival rates in the field compared with controls (P < 0.05) during summer and winter trials. These data suggest that anhydrobiosis in ruminant larvae promotes survival at freezing temperatures, decreases metabolic activity, and prolongs survival under natural field conditions.

Impact of vitamin E or selenium deficiency on nematode-induced alterations in murine intestinal function

The effects of deficiencies in the antioxidant nutrients, vitamin E and selenium, on the host response to gastrointestinal nematode infection are unknown. The aim of the study was to determine the effect of antioxidant deficiencies on nematode-induced alterations in intestinal function in mice. BALB/c mice were fed control diets or diets deficient in selenium or vitamin E and the response to a secondary challenge inoculation with Heligmosomoides polygyrus was determined. Egg and worm counts were assessed to determine host resistance. Sections of jejunum were mounted in Ussing chambers to measure changes in permeability, absorption, and secretion, or suspended in organ baths to determine smooth muscle contraction. Both selenium and vitamin E deficient diets reduced resistance to helminth infection. Vitamin E, but not selenium, deficiency prevented nematode-induced decreases in glucose absorption and hyper-contractility of smooth muscle. Thus, vitamin E status is an important factor in the physiological response to intestinal nematode infection and may contribute to antioxidant-dependent protective mechanisms in the small intestine.

In vitro assessment of the influence of nutrition and temperature on growing rates of five Duddingtonia flagrans isolates, their insecticidal properties and ability to impair Heligmosomoides polygyrus motility

Diverse effects of two temperature regimes (20 and 30 degrees C) on the growing rates of five Duddingtonia flagrans isolates (MUCL 28429, CBS 143.83, CBS 561.92, CBS 565.50, and CBS 583.91) propagated on two liquid (MM, LB) and four solid substrates (CMA, SAB, SAB-GM, and SAB-HP) were observed. All D. flagrans isolates were able to produce chlamydospores but not on all substrates. None of the isolates produced trapping nets and conidia under applied growing conditions. D. flagrans isolates showed moderate insecticidal properties against Galleria mellonella larvae with mortality rates below 20%. Preincubation (18 h) of Heligmosomoides polygyrus infective (L3) larvae in fungal homogenates highly impaired in vitro spontaneous motility of nematodes. This may indicate the potential of D. flagrans bioactive substance(s) for use as biocontrol agents of parasitic nematodes.

[Apoptosis in the regulation of immune response in mice infected with Heligmosomoides polygyrus]

An unbalanced Th1 and Th2 cell subsets response was proposed as the main downregulating mechanisms operating in mice infected with H. polygyrus. During worm infections nonspecific inflammatory and specific immune reactions which might be regulated by apoptosis, coordinate the host protective response. The intensity of apoptosis and proliferation of lymphocytes, the concentration of Th1 and Th2 related cytokines were measured in BALB/c and C57BL6 mice on day 3, 6, 12, 24, 30 after infection with H. polygyrus. Mesenteric lymph nodes (MLN) and popliteal lymph nodes (PLN) lymphocytes underwent an apoptosis, with a different kinetics to the proliferation. Interleukine 5 and IL-6 concentrations increased on time when apoptosis was reduced. No changes in the level of IL-12 were related to intensity of proliferation or apoptosis in both examined strains of mice.

Dependence of IL-4, IL-13, and nematode-induced alterations in murine small intestinal smooth muscle contractility on Stat6 and enteric nerves

IL-4 and IL-13 promote gastrointestinal worm expulsion in part through effects on nonlymphoid cells, such as intestinal smooth muscle cells. The roles of Stat6 in IL-4-, IL-13-, and parasitic nematode-induced effects on small intestinal smooth muscle contractility were investigated in BALB/c wild-type and Stat6-deficient mice treated with a long-lasting formulation of recombinant mouse IL-4 (IL-4C) or IL-13 for 7 days. Separate groups of BALB/c mice were infected with Nippostrongylus brasiliensis or were drug-cured of an initial Heligmosomoides polygyrus infection and later reinfected. Infected mice were studied 9 and 12 days after inoculation, respectively. Segments of jejunum were suspended in an organ bath, and responses to nerve stimulation and to acetylcholine and substance P in the presence and absence of tetradotoxin, a neurotoxin, were determined. Both IL-4 and IL-13 increased smooth muscle responses to nerve stimulation in wild-type mice, but the effects were greater in IL-13-treated mice and were absent in IL-13-treated Stat6-deficient mice. Similarly, hypercontractile responses to nerve stimulation in H. polygyrus- and N. brasiliensis-infected mice were dependent in part on Stat6. IL-13, H. polygyrus, and N. brasiliensis, but not IL-4, also increased contractility to acetylcholine by mechanisms that involved Stat6 and enteric nerves. These studies demonstrate that both IL-4 and IL-13 promote intestinal smooth muscle contractility, but by different mechanisms. Differences in these effects correlate with differences in the relative importance of these cytokines in the expulsion of enteric nematode parasites.

Effects of intestinal nematodes during lactation: consequences for host morphology, physiology and offspring mass

Sublethal parasites are often assumed to have no detrimental effects on their host. However, the sublethal intestinal nematode Heligmosomoides polygyrus affects both the morphology and the physiology of its laboratory mouse (Mus musculus) host and therefore has the potential to affect host life history. The objectives of the present study were to determine (1) whether lactating and non-lactating mice responded similarly to experimental infection with H. polygyrus and (2) whether the changes in morphology and physiology that occurred with parasite infection affected host reproductive performance. Parasitized mice had greater whole body mass as a result of greater lean mass compared with unparasitized mice. Parasitized mice had larger organs (spleen, stomach, cecum and small intestine) and a diminished rate of glucose transport by the small intestine compared with unparasitized mice. Lactating mice had larger organs (liver, kidney, spleen,heart, stomach, large intestine, cecum and small intestine), lean mass and whole body mass, but a similar rate of glucose transport compared with virgin mice. Resting metabolism increased with lactation but not with parasitism. Lactating and non-lactating mice responded similarly to parasite infection for most measured variables. Production of large litters was followed by production of small litters for parasitized but not unparasitized females. After adjusting for parity and litter size, parasitized mothers produced female pups that were 6% smaller at weaning than female pups from unparasitized mothers, but there was no effect of maternal parasite infection on mass at weaning for male pups. Other measures of reproductive output were not affected by parasite infection.

Maternal and direct effects of the intestinal nematode Heligmosomoides polygyrus on offspring growth and susceptibility to infection

The laboratory mouse (Mus musculus) has a naturally occurring intestinal nematode (Heligmosomoides polygyrus) that induces an immune response, causes phenotypic plasticity in metabolism and in organ structure and function, and results in changes in host reproductive output. The objectives of the present study were to determine (1) whether pups infected with parasites at weaning grew differently and had a different body composition at adulthood compared with uninfected pups, (2) whether offspring from parasitized mothers grew differently and had a different body composition at adulthood compared with offspring from unparasitized mothers, (3) whether parasite effects on body composition of pups varied under different infection intensities and (4) whether maternal parasite infection affected susceptibility, duration and intensity of offspring parasite infection. H. polygyrus had direct and maternal effects on offspring growth, but final adult mass was not affected by parasites. Parasite infection in offspring had no effect on overall fat mass, but mass changes for some organs were greater for mice that had a high infection intensity compared with mice that had a low infection intensity. Only offspring from parasitized mothers cleared their parasite infection; however, if the infection was not cleared, the final infection intensity was greater for offspring born to parasitized mothers than to unparasitized mothers. This study shows that chronic, sublethal parasite infection with H. polygyrus has both maternal and direct effects that induce physiological changes in growing mice sufficient to alter host growth trajectories, morphology and susceptibility to parasite infection.

Female mice mate preferentially with non-parasitized males

If parasitic infection is a driving force in female mate choice, then females should preferentially select parasite-free males. The role of infection on female mate choice in mammals was assessed using a 3-chambered apparatus. A female CD-1 mouse was allowed to choose between 2 tethered male mice, 1 uninfected and 1 infected with 200 larvae (L3) of the intestinal nematode Heligmosomoides polygyrus. Both uninfected and infected males were equally receptive to the oestrous females, and females did not differ in the number of visits and time spent exploring the 2 males. Female time preference was not a useful predictor of ultimate mate choice, whereas first mount preference of the female was a reliable indicator. Results indicate that female mice preferentially mated with uninfected males as evidenced by first ejaculation choice, but that male infection status did not significantly affect female reproductive success. Interestingly, litters sired by infected males contained a significantly higher percentage of females suggesting that parasite-induced hormonal changes may alter the sex ratio of the offspring. This study provides the first direct evidence of the impact of parasitic infection on mammalian mate choice.

Acid phosphatase activity in excretion/secretion products from Heligmosomoides polygyrus adults: an indicator of the physiological status of the worms

Acid phosphatase (AP) activity was detected in 24 h culture media from adult Heligmosomoides polygyrus. Female and male excretion/secretion products showed similar specific activity. For both, the AP had a pH optimum of 4.0 and was inhibited by sodium fluoride, tartaric acid, and sodium orthovanadate. The release of AP by adult worms was significantly inhibited by adverse incubation conditions (temperatures of 20 degrees C and 4 degrees C), known physiological perturbers ( t-butylhydroperoxide and sodium azide), and broad spectrum anthelmintics (albendazole, levamisole, morantel, and ivermectin). These results indicate that the AP activity level in the culture medium may be an indicator of the physiological status of the worms.

[Changes in the immune response of BALB/c mice coinfected with Heligmosomoides polygyrus and Trichinella spiralis]

The influence of Heligmosomoides polygyrus on infection with Trichinella spiralis was studied in BALB/c mice. Mice coinfected with T. spiralis and previously given H. polygyrus harboured both nematode species till day 34. The number of T. spiralis muscle larvae was greater in mice coinfected with H. polygyrus/T. spiralis or T. spiralis/H. polygyrus than after infection with T. spiralis alone. Infection with H. polygyrus did not enhance eosinophil and IL-5 levels induced by T. spiralis. Additionally, the production of IgG1 specific to L1 T. spiralis was inhibited by co-infection. Changes in the levels of IFN-gamma and IgG2a implicated a disturbance in Th2 cell activation during protective response and resulted in the greater number of T. spiralis muscle larvae in coinfected mice.

The in vitro secretion of acetylcholinesterase by adult stages of Heligmosomoides polygyrus: the effects of broad-spectrum anthelmintics

The secretion of acetylcholinesterase (AChE) by female and male Heligmosomoides polygyrus was studied in different in vitro culture media. AChE secretion was increased in the presence of fetal calf serum or bovine serum albumin (BSA). In the absence of crowding effects, specific AChE activity in excretion/secretion products was higher for male (2.41 +/- 0.07 mumol min-1 l-1 mg-1) than for female (0.56 +/- 0.04 mumol min-1 mg-1) worms but on a per nematode basis both sexes showed comparable rates of secretion. Acetylthiocholine iodide was the favoured substrate of the enzyme. When the nematodes were incubated in vitro with albendazole (ABZ), ricobendazole (RBZ), mebendazole (MBZ), levamisole (LVM), morantel (MRT) or ivermectin (IVM), at concentrations from 1 mM to 10 nM, in RPMI medium for 2 or 6 h and then transferred to a drug-free medium (RPMI medium supplemented with 0.5% BSA) for 24 h or continuously exposed to the drugs in supplement-free medium (24 h), the concentration- and time-dependent inhibitory effects on AChE secretion were observed. The continued exposure to the drugs for all incubation periods (with a single exception for LVM 1 mM) produced the highest levels of inhibition. Under these conditions, the concentrations inhibiting the secretion of AChE by 50% (IC50) relative to drug-free controls were estimated. The IC50 values ranged from 0.012 microM (IVM) to 2.96 microM (MRT). The potential of this bioassay for the selective primary evaluation of new compounds with broad-spectrum anti-nematodal activity is discussed.

Epidemiology and genetic variability of two species of nematodes (Heligmosomoides polygyrus and Syphacia stroma) of Apodemus spp

The epidemiology and genetic variability of 2 parasitic nematodes Heligmosomoides polygyrus and Syphacia stroma of Apodemus spp. were investigated. Both are parasites of the same host, exhibit a direct life-cycle and are dioecious. However, H. polygyrus has a diploid and S. stroma a haplodiploid mode of reproduction. Haplodiploidy may lead to a more female biased sex ratio and reduced genetic variability. Levels of genetic diversity were analysed using both isoenzyme electrophoresis and RAPDs (random amplified polymorphic DNA). Both parasites showed a female biased sex ratio with a stronger bias for the haplodiploid parasite. Results showed significantly fewer genetic polymorphisms as measured by RAPDs for the haplodiploid parasite S. stroma in comparison with H. polygyrus. Despite the observed female biased sex ratio this could not be explained by a significant amount of inbreeding. Heterozygote deficiency for individual allozyme loci--which could indicate inbreeding--was not found in either parasite species. Other features of the particular life-history of these species are likely to have an impact on the sex ratio and genetic variability too.

Parasitized female mice display reduced aversive responses to the odours of infected males

The present study showed that parasites influence both the responses of uninfected females to males and the responses of female hosts to infected males. In female laboratory mice one of the consequences of exposure to the olfactory cues associated with an infected male was a reduction of the reactivity to a thermal surface, i.e. pain inhibition or analgaesia. Uninfected oestrous and non-oestrous female mice displayed marked analgaesic responses after exposure to the odours of males infected with either the enteric single-host nematode parasite, Heligmosomoides polygyrus, or the protozoan parasite, Eimeria vermiformis. The uninfected oestrous females distinguished between infected and physically stressed males, displaying a greater analgaesic response to the odours of infected males. These analgaesic responses and their anxiety/ fearfulness-associated behavioural correlates could elicit either a reduced interest in, or avoidance of, parasitized males by females. Oestrous female mice infected with H. polygyrus displayed a reduced analgaesic response to the odours of the infected males and differentially responded to the odours of males infected with either the same (H. polygyrus) or a different parasite (E. vermiformis). An exposure time of 1 min elicited minimal responses to the odours of males infected with the same parasite, H. polygyrus, and an attenuated, though significant, non-opioid peptide-mediated analgaesic response to males infected with E. vermiformis. An exposure time of 30 min elicited similar markedly reduced endogenous opioid peptide-mediated analgaesic responses to the odours of both of the categories of infected males. The responses to the odours of a stressed male were, however, unaffected by the parasitic infection. The reduced analgaesic responses of the parasitized females to the odours of infected males may involve either enhanced odour familiarity and responses to group odour templates and/or neuromodulatory shifts resulting in reduced fearfulness and potentially greater interest in the infected males.

The role of lipid content in the infectivity of third-stage larvae of Heligmosomoides polygyrus

The concurrent effects of aging on the lipid content of third-stage larvae (L3) of H.p. polygyrus and H.p. bakeri were described experimentally. It was shown that larval age was closely correlated with their infectivity. The infectivity of H. polygyrus in field and laboratory mice, as indicated by mean worm recovery, was significantly higher for one week old compared with 16 weeks old larvae. Image analysis has been used for the first time to quantify the lipid content of L3 of H. polygyrus with age. The proportion of lipid within infective larvae was reduced and their infectivity declined with age. It has also been found that larvae of H.p. polygyrus possess more lipid than H.p. bakeri suggesting that L3 larvae of H.p. polygyrus are physiologically different from those of H.p. bakeri and the additional lipid reserves assist in extending their survival time in the extremes of climatic conditions in the field.

In vitro assessment of the influence of nutrition, temperature and larval density on trapping of the infective larvae of Heligmosomoides polygyrus by Arthrobotrys oligospora, Duddingtonia flagrans and Monacrosporium megalosporum

The influence of nutrient level, temperature and larval density on the trapping of Heligmosomoides polygyrus L3 by the nematophagous fungi Arthrobotrys oligospora, Duddingtonia flagrans and Monacrosporium megalosporum were investigated by quantification of trapped nematodes. All 3 factors were found to have a significant effect on the number of larvae trapped by A. oligospora and M. megalosporum. Decreased nutrient concentrations resulted in increased trapping for these 2 fungi, but nutrient availability was not found to have a significant effect on trapping by D. flagrans. The 3 fungi were found to have similar responses to temperature, with peak trapping occurring at or near the optimum growth temperatures. Nematode trapping was found to be density dependent for all 3 fungi, with increased percentage trapping at increased larval densities. Comparison in a single experiment of the relative importance of these factors to each fungus showed that nutrient level was the main factor influencing trapping by A. oligospora, whereas D. flagrans and M. megalosporum were more dependent on larval density.

The effects of host population density on the epidemiology of the trichostrongyle nematode Heligmosomoides polygyrus

The present study considers the effect mouse population density on the fecundity, expressed as daily egg output per gram of faeces, and infectivity of the trichostrongyle nematode. Heligmosomoides polygyrus and in the field mouse (Apodemus sylvaticus) and H. p. bakeri in laboratory mouse (CD1). The higher host density resulted in an increased fecundity of H. polygyrus compared with medium and lower host densities. However, the number of H. p. polygyrus and H. p. bakeri recovered 30 days post-infection indicated an increase in worm recovery with increasing host population density. Overcrowding in a host density may affect susceptibility to infection as a result of stress-mediated immunodepression.

Life-history variation among lines isolated from a laboratory population of Heligmosomoides polygyrus bakeri

The extent of variation in several life-history traits within a laboratory population of the parasitic nematode, Heligmosomoides polygyrus bakeri, was studied in 10 relatively inbred parasite lines isolated from a stock population and characterized in BALB/c mice after 4, 8 and 11 generations of isolation. As expected, within-line variation for most traits at generation 11 compared to generation 4 significantly decreased (P < 0.01). At each generation of characterization, variation was observed among lines for parasite establishment, rate of development in the host, rate of early egg production, per capita fecundity, short-term and long-term survival and profiles of egg production, rate of decline in egg production, life-long reproductive effort and in vitro egg hatchability. Measures of all traits, except establishment, were highly repeatable. The rate of development was higher at generation 8 compared to the stock (P < 0.0001), and regression analysis revealed that early egg production of lines increased over 11 generations of isolation (P = 0.003). These results, together with the observed decrease (P < 0.01) in total variation of most of the traits over all lines during the process of isolation, suggested an evolutionary response of the traits, probably to the rapid passage of lines every month. The rate of development subsequently decreased between generations 8 and 11 in all lines (P < 0.0001), suggesting that the random genetic drift procedure used to isolate the lines eventually exerted detrimental inbreeding effects on this trait. The evolutionary responses of life-history traits to rapid passage and inbreeding suggest a genetic basis for variation in these life-history traits.

Heligmosomoides polygyrus: resistance in inbred, outbred, and selected mice

Mice reared selectively as high- and low- immune responders to reinfection with Heligmosomoides polygyrus showed extremes of resistance and susceptibility after infection when compared to inbred BALB/C, DBA/I, CBA, and SJL/J and outbred Quackenbush (Q) mice. The levels of anti-H. polygyrus total IgG and IgG1, IgG2b, and IgG3 isotype antibodies detected in serum from the seven strains of mice after secondary and the eosinophil leucocyte counts in blood after both primary and secondary infections correlated positively and strongly with the levels of protective immunity developed when evaluated using a resistance index formulated from the infectivity, fecundity, and length of adult worms recovered after infection.

Host grooming and the transmission strategy of Heligmosomoides polygyrus

Grooming behavior may play a part in the transmission of the gastrointestinal nematode, Heligomosomoides polygyrus in the mouse host. After infective larvae are placed on individually housed mice, significantly higher numbers of adult worms were recovered from the small intestine of mice that were allowed to self-groom when compared to infection levels in mice that had been fitted with Elizabethan collars to prevent self-grooming. Larvae placed on a single mouse housed with 3 other untreated mice resulted in all mice in the group becoming infected, suggesting that allogrooming may also be important in parasite transmission. A significantly higher percentage of larvae nictate on rough surfaces such as damp peat moss substrate when compared to smooth surfaces such as 0.5% agarose. Mice exposed to larvae placed on peat moss substrate have significantly higher infection levels when compared to mice exposed to larvae on a 0.5% agarose substratum, suggesting that natural transmission of infective L3 larvae in mice may be dependent on a substratum type that allows nictation behavior. A significantly higher percentage of worms were attracted to mouse urine and mouse and rat epidermal lipids when compared to deionized water controls in an in vitro preference assay, suggesting an attraction to host-specific signals. These results support the hypothesis that transmission of this parasite is an active process involving movement of the infective larvae of H. polygyrus into the host's active space where they are ingested during grooming behavior.

Rhythmicity of egg production by Heligmosomoides polygyrus in wild wood mice, Apodemus sylvaticus

The rhythmicity of egg production by Heligmosomoides polygyrus (Nematoda) in wild caught wood mice (Apodemus sylvaticus) was studied. Faecal production followed a 24 h cycle, with peaks at 0400 h and troughs at 1300-1900 h. The patterns in eggs per gram of faeces (EPG) and total eggs were similar to each other, though the former was more accentuated. Both of these followed a 24 h cycle, with peaks coinciding with troughs in faecal production and vice versa. Faecal weight was inversely correlated with EPG, but was not significantly correlated with total eggs. The pattern in EPG presumably reflected the effect of faecal production on the total eggs excreted in each 3 h period. The observed cycle in total eggs probably describes the pattern of egg production by the worm, although other factors, such as the host's intestinal rhythms, may contribute to this cycle.

The food resource of adult Heligmosomoides polygyrus in the small intestine

The aim of this study was to identify the food resources of Heligmosomoides polygyrus, a gastrointestinal nematode of mice. Gastrointestinal nematodes obtain food from 1 of 3 compartments: host ingesta, blood, or intestinal tissue. A method was developed to label these compartments differentially in the living host using 2 fluorescent marker dyes and to record in situ feeding activity of the parasite. Fluoresbrite is a yellow-green fluorescent dye bound to small-diameter beads that are membrane impermeable. Thus, it is restricted to the bloodstream when introduced there, or it remains in the ingesta when fed to the host. Rhodamine B, a red fluorescent dye, is membrane permeable and stains tissue cytoplasm. These dyes were fed to or injected into the bloodstream of the host. Following treatment, the worms were removed, and the contents of the worm intestines were examined by fluorescent microscopy. Worm intestinal contents only fluoresced with rhodamine B dye. These results suggest that H. polygyrus adults feed on tissue in the living host and not on host ingesta or blood.

Chitinolytic activities in Heligmosomoides polygyrus and their role in egg hatching

The occurrence of chitin in the eggshell of Heligmosomoides polygyrus has been determined by histochemical and biochemical techniques. Approximately 5% of the egg dry weight was chitin. Staining with Calcofluor white showed the chitin in the eggshell to be more accessible to the stain after hatching or rupturing of the eggshell. Chitinolytic activity has been detected using fluorescent substrates in extracts of adult males (at low levels), females and eggs. Enzyme activity in situ, within the developing larvae, was visualised with the same substrates. It was localized in discrete granules about 1 micron in diameter which occurred as groups in areas of about 5 microns in diameter, in the posterior third of the larvae. The chitinolytic activity in the eggs increased with the age of the egg and was released into the medium when the eggs hatched. The chitinase activities were very sensitive to inhibition by allosamidin, a specific chitinase inhibitor, with an IC50 for the crude egg extract of 2.2 nM. However, treatment of eggs with 250 microM allosamidin resulted in a slowing but not cessation of egg hatching.

Marginal zinc deficiency has no effect on primary or challenge infections in mice with Heligmosomoides polygyrus (Nematoda)

The effect of low dietary zinc on the survival of an intestinal nematode (Heligmosomoides polygyrus) was investigated in two experiments. In experiment 1 (primary infection), outbred CD1 mice were infected once only with 100 H. polygyrus larvae. In Experiment 2 (challenge infection), mice were given a primary infection that was terminated after 9 d using an anthelmintic drug; the mice were reinfected 5 d later. This protocol stimulates host immunity to the second parasitic infection. Three dietary treatments (control, 60 mg Zn/kg diet; zinc-restricted, 5 mg Zn/kg diet; and energy-restricted, 60 mg Zn/kg diet) were used for both experiments. Both infected and uninfected mice were included within each dietary treatment to control for the effect of parasitic infection on host nutritional status. Plasma zinc concentrations were significantly lower in mice fed the zinc-restricted diet, compared with mice fed the control or energy-restricted diets in both experiments; there were no significant differences in plasma alkaline phosphatase activity or tissue zinc concentration. The significant reduction in plasma zinc had no significant effect on worm burden or egg production of H. polygyrus in either experiment, indicating that the 30-40% reduction in plasma zinc was not sufficient to modify parasite numbers. However, the parasite did affect host nutritional status. Spleen weight was significantly higher in infected mice in both experiments. Following the challenge infection, both liver and spleen copper concentrations were significantly higher, and spleen iron concentration significantly lower, in the infected compared with the noninfected mice.

Genetic variation and host-parasite relations: Nematospiroides dubius in mice

Our work deals with aspects of the genetics and immunology of host-parasite relationships as they influence the development of protective immunity and the phenomenon of coevolution. The aim is to understand parasitism through analyses of host specificity. In earlier studies we examined the inheritance of resistances in mice to infections with Nematospiroides dubius (=Heligmosomoides polygyrus) and established the predominant role played by antibodies in protective immunity. Here we report information concerning the selection of lines of N. dubius that differ in their ability to survive antagonistic immunological reactions from mice. Challenge infections with groups of these mice, immunized and protected by previous repeated infections, show that worms selected to survive the immunity that kills other worms do so by inhibiting the effectiveness of the cellular rather than humoral elements of protective immunity.

Heligmosomoides polygyrus: CD4+ but not CD8+ T cells regulate the IgE response and protective immunity in mice

Oral inoculation of BALB/c mice with infective larvae of Heligmosomoides polygyrus resulted in chronic infection characterized by the release of parasite eggs in the feces for several months. The actual number of eggs per gram of feces was dependent on the dose of the inoculum. Serum IgE in infected mice peaked at a level of greater than 70 micrograms/ml during Weeks 3 through 6 following inoculation, and high levels of IgE (greater than 40 micrograms/ml) persisted for over 14 weeks. Protective immune responses resulted in reduced egg production and the development of markedly fewer adult worms in the small intestines following a challenge inoculation. The role of CD4+ and CD8+ T cells in these responses was examined by depletion in vivo of either T cell subpopulation with rat mAb specific for the appropriate determinants. Mice treated with anti-CD4 during a primary infection had increased EPG which was due primarily to an increase in worm fecundity (eggs produced per adult female). A challenge inoculation of mice that had been cleared of the primary infection with an anthelmintic drug induced a protective response that reduced development of new adult worms by 70-80% and their fecundity by greater than 90%. This protective response was abrogated by injection of mice with anti-CD4. Serum IgE diminished when adult worms were removed after anthelmintic treatment. A more precipitous drop in serum IgE followed successive treatments of mice with an anthelmintic and anti-CD4. In addition, the anamnestic serum IgE response to a challenge inoculation was reduced by over 80% in anti-CD4-treated mice. Anti-CD8 treatment had no appreciable effect on the immunological or parasitological parameters measured following a challenge inoculation with H. polygyrus. Thus, CD4+ T cells regulate host protective immunity, worm fecundity, and IgE levels in an H. polygyrus infection. This experimental system may be particularly suitable for analysis of chronic nematode infections of humans and livestock because of the responsiveness of the parasite in vivo to changes in host immune function.

Host specificity of and cross-immunity between two strains of Heligmosomoides polygyrus

The infectivity of wild and laboratory strains of Heligmosomoides polygyrus (Nematospiroides dubius) in laboratory mice and in three species of wild British rodent was compared. Wild strains, of the subspecies H. p. polygyrus, were isolated from wild caught Apodemus sylvaticus. Only very low-level infections of the wild strains became established in laboratory mice. Similar worm burdens of the laboratory strain became established in laboratory mice and A. sylvaticus, although infections in A. sylvaticus were more short lived. Cortisone treatment of hosts increased the establishment and survival of the heterologous worm strain to that of the homologous strain. In contrast, neither strain of parasite established in Clethrionomys glareolus or Microtus agrestis, and cortisone treatment of C. glareolus did not increase establishment. Infection of laboratory mice with the wild-strain parasite induced significant immunity to a challenge infection with the laboratory strain.

Heligmosomoides polygyrus: effect of exogenous steroid hormones on egg output in vitro

The effect of exogenous steroid hormones on the egg output of Heligmosomoides polygyrus (Nematoda: Trichostrongylidae) was examined in vitro. Using worms raised in female mice, it was found that estradiol, testosterone, and cortisone each significantly decreased egg output. Although similar trends were found using H. polygyrus raised in male mice, none of the decreases found was significant. No significant differences were found with ecdysone or progesterone treatments using worms from female or male mice. Treatment of worms with cortisone did not significantly affect retention of eggs within the uterus of H. polygyrus. Titration of the effect of cortisone on egg output indicated that levels of reduction were significant for concentrations of 5.6 x 10(-6) M to 5.6 x 10(-3) M in worms from female mice and for concentrations of 5.6 x 10(-8), x 10(-7), x 10(-5) and x 10(-3) in worms from male mice. Radioisotope labelling experiments showed incorporation of 3H-corticosterone in the nucleus of intestinal cells of H. polygyrus suggesting that its effect on egg production may be via a modulatory effect on the intestinal cells.

Simple micromotility recorder for rapid screening of potentially anthelmintic compounds

A simple micromotility recorder for monitoring the motility of small nematodes (adult) is described. Normal motility of Ancylostoma ceylanicum and Nematospiroides dubius was recorded. The time course to cause paralysis (paralysis time) was also observed in the presence of various anthelmintics, e.g., Levamisole, Pyrantel; and Ivermectin at graded concentrations. This is a simple in vitro model for screening of potential anthelmintic compounds.

Predisposition of mice to Heligmosomoides polygyrus and Aspiculuris tetraptera (Nematoda)

The purpose of this study was to determine whether predisposition to Heligmosomoides polygyrus and Aspiculuris tetraptera (Nematoda) exists within a naturally infected population of mice. A breeding mouse population was housed in a spacious arena in which endemic infections of H. polygyrus and A. tetraptera were present. H. polygyrus were over-dispersed in the mouse population. Prevalence reached 100% by the age of 3 weeks; intensity of infection increased to a peak in the 10 to 15-week-old mice, and remained high throughout life. A group of 73 mice was treated with pyrantel pamoate, and the expelled worms were counted. Mice were returned to the arena. Daily egg production was monitored 4, 8, 12 and 14 weeks after treatment. Mice were then killed and numbers of H. polygyrus and A. tetraptera were counted. Significant positive correlations were detected between numbers of H. polygyrus at first treatment and at necropsy, indicating the existence of predisposition. Similar results were obtained for A. tetraptera. Correlations improved when data were analysed by age class of mice. Analyses based on egg-count data during reinfection did not support the hypothesis of predisposition, however. A. tetraptera and H. polygyrus burdens were significantly correlated only in 3 to 4-week-old mice at the time of the treatment.

In vivo and in vitro egg production by Nematospiroides dubius during primary and challenge infections in resistant and susceptible strains of mice

Experiments were conducted to examine adult worm burdens, fecal egg output, and in vitro fecundity of Nematospiroides dubius in resistant LAF1 and susceptible CBA mice 12, 15, 18, and 21 days following primary and challenge infections. A strong correlation was obtained on the number of eggs produced by worms cultured in vitro and the egg production as assessed by fecal egg count. Worm counts, fecal egg counts, and in vitro fecundity were similar on all days studied following a primary infection in both mouse strains. However, after challenge infection, LAF1 mice showed lower worm burdens, fecal egg output, and in vitro egg production when compared to CBA mice. Although the egg production of surviving female worms from immune LAF1 mice was decreased, it never fell below a threshold of 100 eggs/day. The reduced fecundity may be a manifestation of a general anti-worm response rather than responses directed specifically at worm reproduction.

Heligmosomoides polygyrus: retarded development and stunting of larvae by antibodies specific for excretory/secretory antigens

The migration of young adult-stage Heligmosomoides polygyrus from beneath the muscularis mucosa to the lumen of the intestine was monitored to compare the rate of development and maturation of larvae in normal and previously infected mice. The development of surviving larvae was significantly retarded in mice that had experienced one or more previous infections and the adult worms arising from a challenge infection were stunted and appeared anaemic. Identical effects were observed with worms recovered from mice that had been injected with immune mouse serum at the time of challenge, and the magnitude of these effects was related to the amount of serum given. Larval maturation was also retarded in mice immunized with larval excretory/secretory (ES) antigens, even though the antibody response was poor due to the very small (submicrogram) amounts of antigen available for injection. In contrast, larvae developed at a normal rate in mice that had been hyperimmunized with killed exsheathed larvae. These mice had serum antibody titres against both "internal" and cuticular antigens similar to those of highly immune (4x-infected) mice, but they had no detectable antibody against ES antigens. The results indicate that the growth and development in vivo of H. polygyrus larvae are retarded by antibodies specific for larval ES antigens. Stunting is permanent, with female worms being affected more severely than males and egg output per worm correspondingly reduced.

The microbial environment and intestinal nematode infections of Heligmosomoides polygyrus in laboratory mice

The difficulty of establishing primary infections of Heligmosomoides polygyrus (= Nematospiroides dubius) in ASH/CSI mice in the Laboratory Animal House at Royal Holloway and Bedford New College during a recent autumn and spring period was associated with a syndrome of worm distortion, together with zero or low worm establishment and reduced fecundity (eggs/female worm). The eggs produced were non-viable and the egg capsule comprised a rumpled lipid and ruptured chitin layer. The egg size and peaks of egg production were also reduced and the total egg output ceased entirely by day 28 post-infection in male mice. The syndrome was repeated when control LACA mice harbouring 'normal' infections of H. polygyrus were housed on the same source of peat bedding material as the ASH/CSI mice. An increase in H. polygyrus egg production in ASH/CSI mice, removed from the peat or treated with 0.04% oxytetracycline hydrochloride suggested that the cause of the syndrome was microbial in origin. A microbiological assay of the peat, which was the common denominator of all syndrome infections, revealed an abundance of chitinase secreting species of bacteria (Bacillaceae). Bacterial chitinase was therefore likely to rupture the chitin layer of the egg capsule producing nonviable eggs and either abnormal or no larvae. Preliminary in vitro studies using chitinase from Streptomyces griseus indicated that the hatching success of eggs of H. polygyrus was reduced as the concentration of chitinase increased.

The tissue reactions of mice to infection with Heligmosmoides polygyrus

The intestines of normal and resistant LAF1 mice were subjected to histologic study to determine the timing and mechanisms of resistance to reinfection by Heligmosmoides polygyrus. During reinfection third-stage larvae are less able to penetrate the intestinal wall. Larvae which are able to encyst develop at a slower rate and provoke an increase in nonspecific inflammation around their cysts. After emergence from intestinal cysts, preadults are rapidly lost, but at no time were injured or destroyed larvae or adults noted. Exsheathed larvae were injected via tail vein into control, sensitized and resistant BALB/c mice. The inflammatory response around entrapped larvae in the lung was measured at 1, 2, 4, and 8 days. A heightened inflammatory response, consisting primarily of polymorphonuclear cells with some round cells which peaked in size on day 2, was observed in both sensitized and resistant mice. A similar heightened inflammatory response was also observed in both AKR (non-resistant) BALB/c (resistant) mice vaccinated subcutaneously with exsheathed larvae.

[Susceptibility of the Chinese hamster (Cricetulus griseus) to parasitic infections. (1). Experimental infection with Nematospiroides (Heligmosomoides) dubius to the cortisone-treated Chinese hamster]

Chinese hamsters (Cricetulus griseus) were experimentally infected with Nematospiroides (Heligmosomoides) dubius. Though they were resistant to the infection of this parasite, they were found to become susceptible to it by the treatment with cortisone. The number of the worms in the intestine of the Chinese hamster and the number of the eggs oviposited by female worms were markedly affected by the doses of the cortisone. Egg oviposition of N. (H.) dubius ceased within 27 days post infection in the cortisone treated Chinese hamster, probably because of the expulsion of the worms. It was suggested that cortisone treatment controlled the infection of the Chinese hamster with N. (H.) dubius and the reproductive activity of this parasite.

The population dynamics of acquired immunity to helminth infection: experimental and natural transmission

Recently we described a mathematical model of the role of acquired immunity in host-helminth interactions. The model gives a good quantitative description of the results of experiments involving the nematode Heligmosomoides polygyrus in laboratory mice. Here we apply the model to the results of two further laboratory studies of the same parasite-host interaction: (i) the repeated experimental infection of a genetically heterogeneous host population, and (ii) the natural transmission of the parasite within mouse populations under different dietary conditions. Numerical simulation again reveals good quantitative agreement between the model predictions and laboratory data. Finally, the model is extended to give a preliminary description of the dynamics of helminth-host interactions of medical and ecological significance in the real world.

An ultrastructural and histochemical study of oogenesis in the trichostrongylid nematode Heligmosomoides polygyrus

Oogenesis in trichostrongylids has been examined for the first time in a light and electron microscopic investigation of Heligmosomoides polygyrus. The female reproductive tract is a single straight tube containing small oogonia (6 micron in diameter), which are arranged in a rosette pattern around a central rachis at the anterior end of the tract. Developing oocytes separate from the rachis and pass posteriorly in single file down the growth zone. Oocytes increase rapidly in volume due to the accumulation of cytoplasmic inclusion granules. These granules are of 3 types. Type 1 granules are amorphous and probably consist primarily of lipoprotein. Type 2 granules are large lipid inclusions and type 3 granules are electron-dense lipoprotein yolk bodies, which are probably used for energy reserves in the developing embryo. Histochemical studies show a more intense reaction for DNA in the nuclei of oogonia than in the nuclei of oocytes. There is a strong reaction for RNA in the nucleoli and in the cytoplasm of oogonia and oocytes. Ultrastructural studies indicate that this RNA is probably in the form of rRNA in the abundant ribosomes. Mature oocytes are cylindrical (60 X 70 micron), have a distinct nucleus with nuclear pores, and the cytoplasm is filled with inclusion granules and ribosomes but contains only small amounts of glycogen. Prior to fertilization the plasma membrane of oocytes acquires a flocculent coat. These oocytes contain 6 distinct bivalent chromosomes in diakinesis. Thus the major changes that occur in developing germ cells are 2-fold: nuclear changes that prepare the chromosomes for fertilization by initiating reduction division, and cytoplasmic changes that involve the synthesis and storage of inclusion granules.

Factors affecting the reliability of the McMaster technique

Factors detracting from the reliability of faecal egg counts based on the McMaster technique include variation in flotation time (interval between loading chamber and counting eggs) and sample dilution (ratio of faecal material to salt solution). We recommend standardization of both these variables as normal laboratory procedure, and propose optima of a 30 minute flotation time and a sample dilution of 15 ml salt solution/g faeces for use of the McMaster technique in the estimation of the fecundity of Heligmosomoides polygyrus (Nematoda).

Faecal egg counts and nematode fecundity: Heligmosomoides polygyrus and laboratory mice

The results are presented of an experimental investigation of the relationship between faecal egg counts and worm burden in outbred MF1 mice infected with Heligmosomoides polygyrus (Nematoda). The sex-ratio of the adult parasites was found to be significantly female biased, but independent of parasite burden. Evidence was also found to suggest a significant association between parasite density and mating success. The linear logarithmic relationship (gradient of approximately 2) between the variance and mean of repeated egg counts from individual mice could not be disrupted by controlled experimental conditions, and is therefore concluded to be an inherent feature of the biology of helminth-host interactions. A significant positive association was detected between host faecal output and parasite fecundity; further investigation of the cause of this association is now required. Average faecal production was found to be inversely related to worm burden. In combination, the above two factors account partly, but not completely, for the observed density dependence in the absolute rate of parasite egg production. Two epidemiological consequences of the relationship between faecal production and parasite fecundity are discussed. First, absolute rates of egg production can only be estimated by temporal egg counts (epd). Secondly, measurements of egg production/g of faecal material (epg) are more reliable indicators of worm burden than measurements of epd. Both faecal output and worm fecundity respond as might be predicted to a period of host food deprivation; faecal egestion and measurements of epd are significantly depressed, and measurements of epg are significantly increased. The data are consistent with the hypothesis that egg production and faecal output are causally associated, but that other factors relating to parasite density also influence egg production. Of the possible causes for the high variability in parasite egg production between mice harbouring low number of worms, the most likely explanation seems to be host heterogeneity (possible genetic in origin). This is discussed in relation to similar patterns observed in data collected from human populations in areas of endemic helminth infection.

Nematospiroides dubius: multiple infections in mice bred for immune responsiveness

Allogeneic mice were reared over 5 generations in a 2-way selection for high (H) and low (L) immune responsiveness to the intestinal trichostrongylid nematode Nematospiroides dubius. After 5 generations of selective breeding, the H mice passed fewer N. dubius eggs and harbored fewer, smaller and less fecund worms than did the L mice. These trends were observed after each of 4 consecutive infections, which were all treated with levamisole before reinfection. Further, more H than L mice were worm-free, and H mice were sensitized to sterile immunity by fewer infections than were needed by the L mice. These results encourage the view that the selective breeding of host species of agricultural importance is a valuable means of biologic control of nematodiasis.

Epidemiology of Heligmosomoides polygyrus in mice: experiments on natural transmission

An experimental system is described for the study of the community dynamics of helminth-host populations, using Heligmosomoides polygyrus in the laboratory mouse. The results of a preliminary experiment using closed populations of 50 mice revealed that coexistence of host and parasite occurs for at least 4 months in the absence of immigration, with the generation of epidemiological patterns similar to those observed in the real world. In well-nourished mice the prevalence and intensity of infection initially increased with time and then declined, probably as a result of acquired immunity. The prevalence and intensity of infection increased less rapidly among hosts fed on a low protein diet, but continued to rise over the entire duration of the experiment. This continued rise is interpreted as evidence of a negative effect of protein malnutrition on host immunocompetence. The frequency distributions of parasite numbers/host were over-dispersed in each mouse population. No density dependence in parasite fecundity was detected. Aspiculuris tetraptera was also found to be present in the mouse populations. This parasite was not transmitted between mice fed on a high protein diet, but rose to a prevalence of 80% in protein malnourished animals. No association between the intensity of A. tetraptera and H. polygyrus could be detected in individual hosts. The results are discussed in terms of the future potential of the system for the investigation of the role of acquired immunity (and its genetic control) in the generation of epidemiological patterns.